Conventionally, an illumination apparatus has been developed to realize an original color of an illumination target. Specifically, it is preferable to make visual performance of various colors of the illumination target closer to visual performance thereof under a reference light. This can be objectively evaluated by using a general color rendering index.
However, the general color rendering index Ra is not enough for an index for evaluating “legibility” of characters written on a paper. Therefore, a chroma value that is calculated by using the simple version of the CIE 1997 Interim Color Appearance Model is known as an index for quantitatively calculating whiteness of a paper from correlation between the whiteness of the paper and the “legibility” of characters.
As for an illumination apparatus for irradiating light of a controlled chroma value, there is known one for irradiating light of a correlated color temperature ranging from 5400K to 7000K (see, e.g., Japanese Patent Application Publication No. 2014-75186).
In the case of using such an illumination apparatus described above as a task illumination apparatus in a low color temperature environment, a large difference in correlated color temperature exists between task illumination light and ambient illumination light and this makes a user uncomfortable. Although the light irradiated from such an illumination apparatus improves legibility of characters, it does not make a user, who is reading a book before sleep, feel relax for a comfortable sleep.